Modern integrated circuit device technology exhibits a temperature inversion effect whereby electrical signal paths are ‘slower’ at cold temperatures than at hot temperatures due to a combination of various MOSFET (metal oxide semiconductor field effect transistor) parameters. In particular, the conjunction of the following parameters, which influence the switching delay within MOSFET devices in different ways, generally contributes to such temperature inversion effects:                Charge carrier mobility (which is a function of T−2, the inverse square of the temperature, at gate bias corresponding to strong inversion);        Threshold voltage (Vth) (which is a function of T−1, the inverse temperature); and        Sub-threshold or leakage current (a function of T);where T represents the temperature.Thus, the characteristics of an integrated circuit device are, at least partly, dependent on the temperature. During the conception of the integrated circuit device, the range of operating temperatures therefore has to be taken into account and the broader the operating temperature range the wider the variation in characteristics to be dealt with.        
The operating temperature is not solely determine by the ambient temperature of the integrated circuit device since normal integrated circuit (IC) device operation causes device ‘self-heating’, i.e. the temperature of the device increases due to the thermal energy released during operation, to a temperature T above the ambient temperature Tamb, absent compensating cooling effects that is. Such self-heating during normal IC operation allows the junction temperature operating range for which an integrated circuit device is designed to be reduced. As a result, faster and easier design closure for the integrated circuit may be achieved. However, during a ‘low power’ period or at start-up of the integrated circuit device, the self-heating capabilities of the integrated circuit device may not be sufficient to be relied upon, e.g. the thermal energy released may not be sufficient to compensate for the loss of thermal energy to the surroundings or the device leading to cooling or the device may not have heated up.